The goal of this proposal is to gain new information about the molecular nature of intercellular recognition and adhesion in early mammalian embryogenesis. Since it would be very difficult to obtain enough normal embryonic material for the biochemical studies proposed, we plan to use teratocarcinoma stem cells, which are closely similar to normal pluripotent embryonic cells, as a source of material. Our working hypothesis is that intercellular recognition and adhesion during early mammalian development is mediated by the interaction of a cell surface carbohydrate-binding component on one cell with its complementary carbohydrate containing receptor on an adjacent cell. We have identified a carbohydrate binding component with fucan/mannan specificity on the surface of teratocarcinoma stem cells. We have also identified a hemagglutinin (lectin) with almost identical specificity present in soluble stem cell extracts. We plan to complete purification of this lectin and to raise an antibody to it. The antibody and other reagents will be used to study the tissue distribution of the lectin during teratocarcinoma stem cell differentiation in vitro, and during the development of early mouse embryos. We also propose to identify the endogenous cell surface carbohydrate-containing receptor for the lectin. In addition, we plan to isolate stem cell variants with altered cell surface lectin and with altered cell surface glycoconjugates (including the receptor) and to study the intercellular adhesion and differentiation of these cell lines.